The key objective of this project is to investigate the stress-strain response of multiphase geomaterials and elucidate the mechanical implications of natural and/or artificial alterations in the state of the pore fluids. The multiphasic connotation of geomaterials makes their pore network a convenient setting for the physical interaction among constituents and plays a crucial role on how these materials deform and fail under stress. Rain infiltration, water table fluctuations and injection/extraction of fluids are only some examples of the remarkable interaction between geological materials and the interstitial fluids. There is therefore a pressing need for predictive theories explaining how changes in volume fractions and pore pressures can generate unexpected failures. The study will be based on the combination of advanced constitutive models for multiphase geomaterials and the mathematical theory of bifurcation. For this purpose, the predictive capabilities of modern modeling approaches will be discussed from a theoretical standpoint, with the goal of identifying the hydro-mechanical mechanisms that can originate failure in geotechnical materials.
This research will contribute to an improved understanding of the mechanics of failure in geomaterials and has the potential to bridge the gap between the mechanical theories for multiphase media and the fundamental concept of material stability. These advances are important to extend to general saturation conditions a series of tools currently available only for fully saturated geomaterials and devise novel strategies for predicting the initiation of unstable mechanisms. The benefits of the research to society will be a better understanding of the mechanisms that govern the occurrence of geo-hazards, novel modeling tools for the design of geotechnical infrastructures and improved predictions of the consequences of multiphase flow across geological formations.
This project has investigated the mechanics of multiphasic geomaterials. The goal has been to elucidate the engineering implications of alterations to the state of the pore fluids, with specific reference to failure events. The project is motivated by the heterogeneous nature of soils and rocks, i.e. solids characterized by multiple fluids within the pore network. The interaction among constituents plays in fact a key role on how geomaterials fail because of fluctuating environmental conditions. There is therefore a pressing need for predictive theories able to explain the origin of failures due to changes in the pore pressure regime of the interstitial fluids. For this reason, the objective of this project has been to formulate innovative theories able to explain the origin of deformation instabilities in this widespread class of natural materials. The long-term goal is to provide the engineering and geoscience communities with new tools for the design and maintenance of civil infrastructures, as well as for the assessment of natural hazards in densely populated areas. From the educational viewpoint, the project has contributed to the academic training of a US female PhD student and an undergraduate student of Civil Engineering. From the scientific viewpoint, the project has focused on the important case of partially saturated geomaterials, i.e. materials in which the pore volume is occupied by a wetting phase (usually water) and a non-wetting phase (usually air). Understanding the mechanics of these materials is indeed crucial to study the stability of any earthen structure interacting with atmospheric processes in the near-surface. The research methodology used throughout the project has involved a combination of analytical studies, computations and validations against experimental data. Such strategy has generated new criteria to assess the robustness of the models currently used for engineering analyses. In addition, it has provided a physical interpretation of the numerical predictions derived from such models, which for the first time has been based on principles of material stability. A notable result of the project has been the identification of analogies between the mathematical methods used for saturated soils and those developed for unsaturated materials. This finding simplifies the integration between the new tools and the available computational infrastructure. At the same time, we have pointed out that a state of partial saturation produces major differences on the mechanisms of interaction between solid and fluid phases, thus requiring specific strategies to predict the spatial and temporal dynamics of failure events activated by changes of the environmental conditions. The tools formulated by the project will benefit the society by generating a better understanding of the mechanisms that govern the occurrence of geo-hazards and the deterioration of civil infrastructures. These benefits are pivotal for the engineering profession, which constantly deals with uncertainties, incomplete or lacking data and conflicting demands from clients, governments and general public. The development of knowledge and technical expertise in this area of engineering has therefore major benefits for both the national and the international community, as new findings in this area can transform the assessment of geological risks and the management of the economic losses associated with infrastructural failures and natural disasters. In addition, given the fundamental nature of the research methodology, the new tools developed by this project find application in numerous neighboring disciplines, such as geophysics, geomorphology, engineering geology, hydrology, urban planning, and material sciences. As a result, the scientific and educational endeavors initiated by this project can be a springboard for the future involvement of Geomechanics research into themes of social relevance, such as the improvement of the public awareness about the implications of infrastructure deterioration, uncontrolled urbanization and development of new energy technologies.
